The carbon fibers excel in specific intensity, specific modulus, flame resistance, heat resistance, and durability. Therefore, a range of application of the carbon fibers thus technically advantageous is increasingly expanding. In recent years, thickened carbon fiber precursor tows including 50,000 filaments or more started to be used in order to improve the productivity of carbon fibers for cost reduction. In consequence of the ongoing trend, any packaged tow with such a thickened fiber tow is inevitably enlarged in size. An advantageous way to manufacture the packaged tow thus upsized is to throw the tow into a packaging container. So far were invented and disclosed variously different tow throw-in packaging techniques.
Japanese Patent Application Laid-Open No. 2006-176328 (Patent Document 1) discloses such a packaging technique. According to the packaging method disclosed in the Patent Document 1, a moisture-contained carbon fiber precursor tow having a large degree of fineness of 48,000 dtex to 720,000 dtex and a flame-proofed carbon fiber precursor tow (hereinafter, the carbon fiber precursor tow and the flame-proofed carbon fiber precursor tow are both simply called carbon fiber precursor tow) are thrown into a packaging container through a tow throw-in shoot, and a press plate on standby at a position above an end on the side of a folded end is pressed down when the packaging container reciprocated in a tow-width direction arrives at a folded end on the other side to compress the tows to obtain a packaged tow. The technique of the Document 1 is particularly characterized by setting a storage bulk specific gravity of the carbon fiber precursor tow thus packaged to at least 340 kg/m3.
Japanese Patent Application Laid-Open No. 2008-121147 (Patent Document 2) discloses a packaging technique similar to the method disclosed in the Patent Document 1. According to the packaging method, a tow throw-in shoot is elevated relative to a packaging container as a tow throw-in top in the packaging container rises to a higher level. The method is particularly characterized in that a distance a (mm) between a lowest position on a tow lead-out end and the tow throw-in top, a thickness h (mm) of a press plate, and a minimum distance y (mm) between the press plate and the tow throw-in shoot meet a relationship expressed by the formulas; 10≦a≦400, and (a-h)/y≦3.3, when a total degree of fineness of the tow is at least 48,000 dtex to less than 180,000 dtex.
The carbon fiber precursor tow thus packaged in the packaging container is not infinitely continuous but has a finite length, therefore, it is not possible to directly flame-proof and carbonize different tows in succession. In fact, the flame-proofing and the carbonization processes have to be suspended every time when these processes for the tow in one packaging container are over. The technical disadvantage resulted in the development of a piecing work to obtain a string of continuous tow by connecting front and back ends of tows. With this technique, the tow can be continuously flame-proofed and carbonized.
A long and continuous tow obtained by the piecing work still possibly undergoes a problem; thread breakage at joined parts of the tows due to heat accumulation particularly in the flame proofing process which generates heat. This sometimes interrupts the flame-proofing and carbonization processes desirably continuously performed. As disclosed in Japanese Patent Application Laid-Open No. 2008-150733 (Patent Document 3), for example, a thread breakage preventing technique performed prior to the piecing work was developed, wherein ends of the tows, at which the tows are joined with each other, are flame-proofed in advance.
It is disclosed in, for example, Japanese Patent Publication 47-51979 (Patent Document 4) that when a yarn continuously supplied, such as synthetic-fiber filament yarn, spanned yarn, or textured yarn, is introduced in a housing container, a front end thereof is led out of the container, ends of the yarn at its front and back are fixed to an outer surface of the housing container, and the front end of the yarn is joined with a back end of a yarn introduced in another housing container.
It is disclosed in the Patent Document 5 (Japanese Patent Application Laid-Open No. 2002-138326) that a fiber tow is cut as soon as a corrugated board box or a can is fully filled with fiber, and the cut end is knotted to prevent unraveling of the tow, or a clip-like member is applied to the tow end to prevent unraveling of the tow end.